import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<MutableKeys<{ a: number, readonly b: string }>, 'a'>>,
  Expect<Equal<MutableKeys<{ a: undefined, readonly b: undefined }>, 'a'>>,
  Expect<Equal<MutableKeys<{ a: undefined, readonly b?: undefined, c: string, d: null }>, 'a' | 'c' | 'd'>>,
  Expect<Equal<MutableKeys<{}>, never>>,
]
